Bullet Jump

[oldmossy]

I had a 7MM RUM built to shoot 195 elite hunters. And it shoots them really good. But the speed and killing effectiveness isn't that of the 180 hybrids that I shot for years. Running through different powder charges, we couldn't get the groups any better than 1 inch @ 100yds using the 180 hybrids. We didn't adjust seating depth, because we cant get to the lands with the 180s. My question is- How much effect does adjusting seating depth have when youre already jumping a considerable distance to the lands?
Im not a reloader, my buddy does it for me. I'm just wondering if he just didn't want to take the time to develop a load for the 180s. Or if the jump really makes no difference after a certain point.
I'd rather have 180s at 3200 than my 195s at 2930.
I tried researching this prior to asking but never really found a answer.
Thanks

 

[GLTaylor]

Different jump can definately impact a rifle's grouping. Every barrel is different.
Hybrid designs are usually less jump sensitive than vlds and similar.
However - you have to test your rifle.
Look at Berger's recommendations.
I have rifles that shoot best with jumps ranging from .020 to .120!

 

[nksmfamjp]

Good question.....that said, I think we get crazy about seating to the lands and forget about the basics.

I have a 300 WSM that can barely hold the bullet when touching the lands. That said, I messed around with seating depth and saw little change. Working on concentricity made a big difference. For seating depth, I found getting the boat tail/bearing surface junction about even with the base of case neck to give about best accuracy for some reason. Also, mag length was good too.

My jump is about 0.15" in this chamber....for reference.

 

[338 dude]

I had a 7MM RUM built to shoot 195 elite hunters. And it shoots them really good. But the speed and killing effectiveness isn't that of the 180 hybrids that I shot for years. Running through different powder charges, we couldn't get the groups any better than 1 inch @ 100yds using the 180 hybrids. We didn't adjust seating depth, because we cant get to the lands with the 180s. My question is- How much effect does adjusting seating depth have when youre already jumping a considerable distance to the lands?
Im not a reloader, my buddy does it for me. I'm just wondering if he just didn't want to take the time to develop a load for the 180s. Or if the jump really makes no difference after a certain point.
I'd rather have 180s at 3200 than my 195s at 2930.
I tried researching this prior to asking but never really found a answer.
Thanks

I don't use my chronograph until I found a good load the main reason for this is people get hung up on a number get a load your rifle shoots and go with it and what you were saying a couple hundred feet per second a difference of 15 grains in the projectile you should plug both of those into a ballistic program and see about the energy down range I bet they are much closer than you think

 

[Tiny Tim]

Do a seating depth test. If your limited by mag length, start there and work in. I have a 300 wm that shoots best at .090" off the lands and a 243AI that likes .010" off. Every gun is different, and some bullets don't seem to work in some barrels no matter what you do. Even powder/bullet combo may have some effect. Steve at Hammer bullets give instructions for his bullets and simply states, if it doesn't shoot moa, try another powder.

 

[L.Sherm]

When you change bullets your gonna have to start completely over with load development.

 

[oldmossy]

Good question.....that said, I think we get crazy about seating to the lands and forget about the basics.

I have a 300 WSM that can barely hold the bullet when touching the lands. That said, I messed around with seating depth and saw little change. Working on concentricity made a big difference. For seating depth, I found getting the boat tail/bearing surface junction about even with the base of case neck to give about best accuracy for some reason. Also, mag length was good too.

My jump is about 0.15" in this chamber....for reference.

Same issue. Same approach. I guess I'll stick with 195s. Thanks guys

 

[oldmossy]

I don't use my chronograph until I found a good load the main reason for this is people get hung up on a number get a load your rifle shoots and go with it and what you were saying a couple hundred feet per second a difference of 15 grains in the projectile you should plug both of those into a ballistic program and see about the energy down range I bet they are much closer than you think

We were testing for a 338 lapua yesterday. And did just that. Put chrono away until we had a good group. Then chronoed to see what speed to enter for ballistic calculator.

 

[CBS]

I'm starting to think that methodology CAN be backwards. I'm leaning toward the idea that es is a better indicator of long range accuracy and consistency than 100 yd group size.

This is a relatively new concept for me as I've had problems working up loads with the ideas you guys are talking about. E.g., I have a 7mm that i worked up a great load that consistently shoots groups in the 3s @100 yds. But because of velocity es my groups at 750 around moa +.

I found some you tube videos by a guy named Erik Cortina. He's an f- class shooter that details his methodology for working up loads. In his load development process he shoots different powder charge weights at a logical seating depth and doesn't care what size groups they shoot. His focus is strictly on low es. Low es results long distance consistency.

After finding his es node he then shoots for groups by seating depth.

I've tried this a couple times and while I don't think I've got my processes down my 100 yd groups aren't as good as I've shot in the past but my 5-700 yd groups are better.

From what I've experienced low es is more important than 100 group size for longer ranges.

 

[oldmossy]

We had big es using chrono. had 1/2 moa at 100yd.( 338 lapua). Shot at 715 yds and kept same 1/2 moa accuracy. Figuring our chrono just not giving accurate speeds. Had a chrono set up on tripod at 10ft from muzzle. Then used a magnospeed(?) that clamps on barrel after we were done to test speeds and didnt show good es either. 60 ft es! But 1/2 moa at 100 and 715. ??

 

[CBS]

Well............if you think that an extreme spread of 60 can produce consistent groups at long range then trying to point out a contrary view is useless.

Plug the high and low into your ballistic calculator and see what the math says. At a 60ft/sec es you CAN'T have a consistent 1/2moa. Doing it once doesn't mean it's consistent.

 

[oldmossy]

Im not disagreeing. Im actually agreeing.. Im actually questioning whether u think u can trust chronograph. Ive ran numbers plenty of times on ballistic calulators

 

[Mcranch]

Same issue. Same approach. I guess I'll stick with 195s. Thanks guys

Same issue. Same approach. I guess I'll stick with 195s. Thanks guys

So would you consider not extending the freebore to the 195 and ream for a 180/185 length projectile ? I don't want to highjack the topic I'm just wanting to get view points to gain info.

 

[Wallie]

Well............if you think that an extreme spread of 60 can produce consistent groups at long range then trying to point out a contrary view is useless.

Plug the high and low into your ballistic calculator and see what the math says. At a 60ft/sec es you CAN'T have a consistent 1/2moa. Doing it once doesn't mean it's consistent.

I would agree that he couldn't have consistent 1/2 MOA at all ranges, but it certainly is possible to shoot tighter that your chrony indicates, his 1/2 MOA at 715 is almost certainly due to positive compensation, be it purposeful or accidental.
When I started handloading I used the Audette ladder exclusively, didn't realize for years that I was tuning positive compensation for the specific range I did my testing at.